Car problem (that sound when driving over motorway stripes)

[RipTrip1]

You know when you drive over painted motorway stripes and you hear that 'WoooooW' noise (best way I can describe it). Well my car is doing that, but only sometimes, but usually when taking a right hand corner. Doesn't even do it on every right hander, I've also heard it once when going over a speed bump.
What's the most likely cause? I've heard wheel bearings but you'd think that would occur all the time, or at least on every right hand bend.